The investigation of structure/property relationships in materials often requires processing prior to the measurement of their properties. Fiber spinning is often the processing method of choice in long chain polymers because of the subsequent chain alignment that occurs during the shear and windup process. This alignment can give rise to highly anisotropic electrical, mechanical and photonic properties. Unfortunately commercial spinning lines need large (5-10 lbs) quantities of starting material in order to produce melt-spun fibers. This limits the candidates for investigation to those that are made in sufficiently large quantities and/or those that do not degrade at elevated temperatures, in the case of melt spinning. Solution spinning is possible as an alternative method but has been reserved for those polymers that dissolve in volatile and often times aggressive solvents (e.g., KEVLAR® in sulfuric acid). (KEVLAR® is a polyamide, in which all the amide groups are separated by para-phenylene groups, that is, the amide groups attach to the phenyl rings opposite to each other, at carbons 1 and 4 and is manufactured by DuPont), in sulfuric acid).
The electrospinning of fibers has been investigated for more than 30 years. However, since 1998 the number of publications on electrospun polymer nanofibers have grown exponentially, Z. M. Huang, Y. Z. Zhang, M. K. Kotaki and S. Ramakrishna, Composites Sci. and Tech. 2003, 63, 2223-2253 (“Huang”), US20030137069. Electrospinning, an offshoot of electrospraying, can be used to spin spider-web type fibers (see FIGS. 1-3) for characterization and testing of their mechanical and surface properties. The fibers produced during the electrospinning process are microscale and nanoscale, with diameters ranging (D. H. Reneker and I. Chun, Nanotechnology 1996, 7, 216 (“Reneker”)) from 40 nm to 5 μm compared to traditional textile fibers which have diameters (Reneker) of 5 to 200-μm. The primary advantage of electrospinning is that it uses minute quantities (as little as 10-15 mg) of polymer in solution to form continuous fibers. Although a number of commodity polymers have already been electrospun (Huang and S. Megelski, J. S. Stephens, D. B. Chase and J. F. Rabolt, Macromolecules 2002, 35, 8456 (“Megelski”), an understanding of the mechanism and parameters that affect the electrospinning process is only starting to emerge. There are a limited number of parameters that appear to effect the fiber diameter, the concentration of “beads”, the fiber surface morphology and the interconnectivity of polymer fibrils. These include solution concentration, distance between “nozzle” and target molecular weight of the polymer, spinning voltage, humidity, solvent volatility and solution supply rate. Although some of these (e.g., molecular weight, humidity) have been investigated in detail (C. Casper, J. Stephens, N. Tassi, D. B. Chase and J. Rabolt, Macromolecules 2004, 37, 573-578 (“Casper”) and Megelski most of the work has focused on investigation of the development of microstructure in fibers and their potential applications ranging from tissue engineering constructs to fuel cell membranes.
Electrospinning is a simple method that can prepare fibers with submicron diameter using electrostatic force. Submicron fibers prepared by this technique have recently come under intense scientific study due to wide ranging potential applications including filtration, optical fibers, protective textiles, drug delivery system, tissue engineering scaffolds, and gas separation membranes etc.
Many polymers, synthetic and natural, have been successfully spun into nano-, and/or micron-sized fibers from polymer solution and melt. Although polyolefin (CH2—CH2)n, poly-α-olefin (CH2—(R—CH))n, with R=aliphatic, aromatic or cyclic groups, their copolymers and/or their polymer blends are important commercial polymers, very limited work on the electrospinning of polyolefins, poly-α-olefins, their copolymers and/or their polymer blend fibers exists. In the case of polyolefins, poly-α-olefins, their copolymers and/or their polymer blends have limited solubility due to their excellent chemical resistance and non-polar structure, and hence are not easy to electrospin from solution. All investigations thus far have used melt-electrospinning.